Liquid ejection apparatus

Abstract

In a liquid ejection apparatus, a controller of the liquid ejection apparatus is configured to, in response to receiving a recording instruction to instruct the liquid ejection apparatus to perform image recording on a recording medium, perform ejection inspection to determine whether liquid is ejected from each nozzle of a liquid ejection head toward an electrode based on a signal outputted from a signal output circuit. For the ejection inspection, the controller is configured to control a voltage applying circuit to apply an inspection voltage between the electrode and the liquid ejection head. In response to detecting that a leakage current greater than a predetermined value flows between the electrode and the liquid ejection head, the controller is configured to cancel the ejection inspection and control a voltage applying circuit to apply a reverse voltage opposite in polarity to the inspection voltage between the electrode and the liquid ejection head.

What is claimed is: 
     
       1. A liquid ejection apparatus comprising:
 a liquid ejection head having an array of nozzles, the liquid ejection head being configured to eject liquid from each of the nozzles; 
 a cap configured to cover the nozzles; 
 an electrode accommodated in the cap; 
 a voltage applying circuit configured to apply a voltage between the electrode and the liquid ejection head; 
 a signal output circuit connected to the electrode; and 
 a controller configured to, in response to receiving a recording instruction to instruct the liquid ejection apparatus to perform image recording on a recording medium, perform ejection inspection to determine whether liquid is ejected from each nozzle toward the electrode based on a signal outputted from the signal output circuit, 
 wherein, to perform the ejection inspection, the controller is configured to
 cause the liquid ejection head and the cap to face each other, 
 control the voltage applying circuit to apply an inspection voltage between the electrode and the liquid ejection head with the liquid ejection head and the cap facing each other, and 
 drive the liquid ejection head to eject liquid from a nozzle of the nozzles toward the electrode, 
 
 wherein, during the ejection inspection, the controller is configured to detect whether a leakage current greater than a predetermined value flows between the electrode and the liquid ejection head based on a signal from the signal output circuit, 
 wherein, in response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head, the controller is configured to cancel the ejection inspection and control the voltage applying circuit to apply a reverse voltage opposite in polarity to the inspection voltage between the electrode and the liquid ejection head. 
 
     
     
       2. The liquid ejection apparatus according to  claim 1 , wherein, in response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during the ejection inspection, the controller is configured to control the voltage applying circuit to apply a reverse voltage that is the same in magnitude as the inspection voltage and is opposite in polarity between the electrode and the liquid ejection head for the same length of time as that of the inspection voltage. 
     
     
       3. The liquid ejection apparatus according to  claim 1 , wherein, in response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during the ejection inspection, the controller is configured to control the voltage applying circuit to apply a reverse voltage that is smaller in magnitude than the inspection voltage and is opposite in polarity between the electrode and the liquid ejection head for a length of time longer than that of the inspection voltage. 
     
     
       4. The liquid ejection apparatus according to  claim 1 , wherein, in response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during the ejection inspection, the controller is configured to control the voltage applying circuit to apply a reverse voltage that is larger in magnitude than the inspection voltage and is opposite in polarity between the electrode and the liquid ejection head for a length of time shorter than that of the inspection voltage. 
     
     
       5. The liquid ejection apparatus according to  claim 1 , further comprising a wiper,
 wherein the liquid ejection head has a nozzle surface defining the nozzles, and 
 wherein the controller is configured to control the wiper to wipe liquid adhering to the nozzle surface after application of the reverse voltage. 
 
     
     
       6. The liquid ejection apparatus according to  claim 1 ,
 wherein, in response to receiving a recording instruction to instruct the liquid ejection apparatus to perform image recording on a recording medium, the controller is configured to perform the ejection inspection and then perform image recording by controlling the liquid ejection head to eject liquid from the nozzles to a recording medium, and 
 wherein, in response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during the ejection inspection, the controller is configured to cancel the ejection inspection, perform image recording by controlling the liquid ejection head to eject liquid from the nozzles to a recording medium, and then control the voltage applying circuit to apply the reverse voltage between electrode and the liquid ejection head. 
 
     
     
       7. The liquid ejection apparatus according to  claim 6 ,
 wherein, in response to detecting that the leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during the ejection inspection, the controller is configured to suspend the ejection inspection and determine whether the number of recording media included in the recording instruction is below a predetermined number, 
 wherein, in response to determining that the number of recording media included in the recording instruction is below the predetermined number, the controller is configured to perform image recording on all the recording media by controlling the liquid ejection head to eject liquid from the nozzles to each of the recording media, and then control the voltage applying circuit to apply the reverse voltage between electrode and the liquid ejection head, and 
 wherein, in response to determining that the number of recording media included in the recording instruction is greater than or equal to the predetermined number, the controller is configured to cancel the ejection inspection and control the voltage applying circuit to apply the reverse voltage between the electrode and the liquid ejection head, and then perform image recording on all the recording media by controlling the liquid ejection head to eject liquid from the nozzles to each of the recording media. 
 
     
     
       8. The liquid ejection apparatus according to  claim 1 , further comprising discharging means for performing a discharging operation in which liquid in the liquid ejection head is discharged from the nozzles,
 wherein, in response to determining that the number of occurrences that the leakage current greater than the predetermined value flows the controller has detected since a discharging operation previously performed is greater than or equal to a predetermined value, the controller is configured to cause the discharging means to perform the discharging operation. 
 
     
     
       9. The liquid ejection apparatus according to  claim 1 ,
 wherein the liquid ejection head has a liquid channel including the nozzles, 
 wherein, in response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during the ejection inspection, the controller is configured to receive information related to whether air is trapped in the liquid channel and determines whether air is trapped in the liquid channel based on the received information, 
 wherein, in response to determining that air is trapped in the liquid channel, the controller is configured to cancel the ejection inspection and control the voltage applying circuit to apply the reverse voltage between the electrode and the liquid ejection head, 
 wherein, in response to determining that no air is trapped in the liquid channel, the controller is configured to determine whether the number of occurrences that the leakage current greater than the predetermined value flows the controller has detected since a previous application of the reverse voltage between the electrode and the liquid ejection head is below a predetermined value, 
 wherein, in response to determining that the number of occurrences is below the predetermined value, resume the ejection inspection, the controller is configured to resume the ejection inspection, and 
 wherein, in response to determining that the number of occurrences is above the predetermined value, cancel the ejection inspection and control the voltage applying circuit to apply the reverse voltage between the electrode and the liquid ejection head.